This invention relates to injecting apparatus for injecting a fluid under pressure, e.g. fuel injecting apparatus for internal combustion engines, apparatus for injecting liquids, e.g. a catalyst into chemical reaction vessels under pressure, and other apparatus for injecting a dose of fluid.
Although the present invention is applicable to any situation where a measured dose of fluid is to be injected under pressure, it will be convenient to describe the invention with particular reference to injecting fuel into an internal combustion engine.
Fuel injectors used in internal combustion engines, including both spark ignition and compression ignition (or diesel) engines generally utilise an external pump for supplying the fuel under sufficient pressure to be injected into the engine cylinder. The timing of the injection point in the engine operating cycle is determined by externally controlling the operation of an injector valve by mechanical means. One disadvantage of providing external pumping and control is the need for the provision and servicing of such external systems.
A general problem with injectors, particularly ones supplied from an external pump, is lack of responsiveness to any faulty condition in the associated cylinder. For example, if a piston ring is broken, known injectors will continue to inject fuel charges into the cylinder. Thus fuel will be exhausted from the engine leading to air pollution by exhausted unburnt fuel.
It has been proposed in the past to utilise the build up of pressure within the cylinder of an internal combustion engine during the compression stroke to provide the motive force to compress fuel within the injector body. For example, there has been proposed a fuel injector which has a body, and a piston which is movable within the body under the action of cylinder pressure. The movement of the piston in the injector body causes an increase in pressure of a fuel charge introduced into the body to a point where the pressure enables a non-return valve associated with the injector nozzle to open and allow the fuel to be injected under pressure into the engine cylinder. Problems with this device include difficulty and uncertainty in closing of the valve leading to fuel continuing to dribble from the injector after the desired cut off point, and also a general lack of control over the operation of the injector.
U.S. Pat. No. 2,516,690 in the name of French shows a fuel injector which utilises the associated engine cylinder pressure to develop the pressure to inject the fuel. The French apparatus has a simple spring biased non-return valve at the injection nozzle so that the opening and closing of the injection nozzle is solely controlled by pressure differential and spring force. Some control of pressure developed is provided by a non-return valve in an outlet from the pumping chamber and an adjustable flow restrictor downstream of the non-return valve. The French apparatus has very limited ability to enable control of the injector operation including timing, injection pressure, volume of fluid injected, and degree of positiveness in action.
U.S. Pat. No. 4,394,856 in the name of Smith also shows an injector using engine cylinder pressure to develop the injecting pressure. The Smith apparatus uses a non-return valve as the injection valve. A solenoid operated non-return valve is provided in the outlet from the pumping chamber and an adjustable flow restrictor is provided in the outlet line downstream of the non-return valve to enable adjustment of the possible rate of flow when the solenoid non-return valve is opened. In a similar manner to the French US patent, the Smith injector has very limited ability to enable control of the injector operation including timing, injection pressure, volume of fluid injected, and degree of positiveness in action.
U.S. Pat. No. 4,427,151 in the name of Trenne shows a similar injector to the Smith injector except that there is provision for adjusting the clearance between the outlet valve member controlled by the solenoid and its associated seat so that that adjustment enables some control of the flow rate for fuel flowing out of the control chamber. As with the French and Smith specifications, the Trenne injector has limited degrees of control and limited positiveness in operation, particularly the non-return injector valve.